Control circuit



`June 184, 1946. w. J. PocH CONTROL CIRCUIT.

vFiled'may 13. 194s INVENTOR. Waldmar A Trae ,v5 Y

Patented June 18, 1946 CONTROL CIRCUIT Waldemar J. Poch, Moorestown, N. J., assigner to Radio Corporation of America, a corporation ci'v Delaware Application May 13. 1943, serial No. 486,788 z claims. (ci. 17a-7.2)

This invention relates to television circuits and is directed particularly to a circuit combination whereby the level of the resultant output video signal is suitably controlled.

As was mentioned in aconcurrently led patent 'application of the same applicant and entitled "Automatic volume control circuits," which application is identified as Serial No. 486,789, it is desirable that the signal level of thetelevision output signal be suitably controlled and its level substantially constant. In television systems wherein the video signals are developed from a scanning action by a cathode ray tube of the socalled storage type, it frequently happens that the signal energy produced during non-scanning periods of the television cycle cannot etllciently be used to provide the automatic volume. control energy because if there is to be a true automatic volume control system, it is desirable that the contro1 eiect be produced only by virtue of the useful video or picture signals. To meet such l described in the prior art which utilize a so-called storage type cathode ray tube to convert4 the optical image of the scene to -be transmitted into video signal energy. Among the types of scan- 'f ning tubes for such purposes are those that have become known in the art as the Iconoscope" and the Orthicon. Each oi' these types of tubes has been described in the literature fully by all of Zworykin, Iams and Rose, and others. and one of such prior art publications is known as that entitled The Orthlcon, a television pick-up tube" which was described by Messrs. Rose and Iams in the RCA Review for October, 1939. Accordingly, no detailed reference to the tube per se will be made herein, except for abroad reference vand statement that the image of -a scene to be transmitted is focused upon the mosaic electrode element of the scanning tube to produce thereon electrostatic charges of magnitudes proportional to the image brightness at its several elemental areas. The produced charges are then neutralized by a scanning cathoderay beam which scans the camera tube mosaic element under the control of suitable defiecting fields, and, by reason of the charge neutralization, the video or picture signals are produced. 'I'hese signals are then t 2 i suitable amplifying units, and, when adequately amplied, are supplied to wire or radio communication channels to actuate suitable image reproducing units.

Since the signal energy thus produced is sub ject to change in level, for various reasons which need not be herein discussed in detail, the presl ent invention has as one of its main objects, that of establishing an automatic volume control unit to provide compensation for signal energy level shifts, which are not due to the character of the transmission itself.

In this application, like in the companion application mentioned, one of the main objects is that of controlling the signal level by an automatic volume control unit which shall not be operative during periods when the usual blanking and sync signals are being transmitted.

Another object of the invention is to provide an automatic volume control unit for television apparatus which is keyed to its operative periods by the presence and absence of the blanking control signals.

A further object of the invention is that of providing a control system of the character described which is eiective directly in the amplifier system and, under some conditions, eiective to modify the general brightness level of the light limage impinging upon the camera tube storage elements so as thereby to vary the output signal level. y

Other objects are those of providing improved operation of television systems over that formof operation now generally known and, at the same time, to provide an operating unit in which the ildelity of operation is improved.

The invention is schematically shown in one vof its preferred forms by the accompanying drawing, wherein the Iconoscope or "Orthicon type of camera tube is shown in a schematic representation at Il. In the production of output video signalling energy, the optical image of anv in the literature and need ynot be described herein in more detail except, possibly, to state that supplied to external utilimtlon circuits, such as Il each may include one or a plurality ofseparate case of the line amplifier 2|, there would almost always be a plurality of stages of amplification in order that the necessary signal gain may be achieved. 'Ihe signal output from the line amplifier 2| is th'en supplied to a further amplifier unit 23, which is generally known as a combining amplifier unit. In this last named amplifier, the blanking and sync signals, which'occur at spaced time intervals, such as at the end of each scanning line and at the end of each scanned field of the picture or scene, are mixed with the video signal output of the pre-amplifier I9. The resultant combination of signals ls then supplied to a further amplifier tube 25, usually called a clipper tube, and controls the current flow therein when supplied to the control electrode element 21.

Signal output energy from the tube 25 is then derived across the cathode resistor 3|, which connects between the tube cathode 33 and ground 35. Suitable bias is obtained on the tube by way of the resistor 31 and thebias source 39.

The signal energy which is supplied to the clipper tube 25 is also supplied to a suitable rectiiler tube, such as the diode 4 I, which has its cathode element 43 connected to be energized by the video signals and the plate or anode element 45 connected to ground 35 through the anode resistor 41.

As was disclosed in the companion case hereinbefore mentioned, it is desirable that the automatic volume control established by virtue of the rectifier tube 4| shall not be effective during periods of blanking and synchronizing, in order that the control effect provided shall be one functioning only in accordance with the video signal. To this end, the blanking signals are supplied at the terminal 49, as well as to the combining amplifier 23. When the blanking signals are applied at terminal 49, they are impressed in negative polarity (as indicated) so that the anode of the diode will be carried highly negative and a condition of cut-oil established in the tube. In this way, the rectifier or diode 4| is keyed to an inoperative state, so to speak, by the blanking signais, and its useful operative period to supply an A V. C. bias is thus restricted to the periods of video signal transmission.

Under the control of the current passing through the diode 4|, a control potential is impressed upon the input electrode of the relay tube 5| through the resistor 52. At the same time, the current flowing in the diode 4| also establishes a bias level upon the clipper tube 25, so that its output may be automatically varied by the control signal. Under the control ofthe current flow in the relay tube 5I, a bias voltage may be impressed upon a selected tube of the line amplifier unit 2| through the resistor 52, assuming the switch arm 56 to be in a position against th'e upper contact 51, as shown, and bias supplied by a bias source 56. In this way, the output from the amplifier 2| is suitably controlled by way of the bias established upon it from the rectifier or diode element 4|.

Under some conditions of operation it may be desirable to establish a control of the video signal production itself. This could occur, for instance, where the output signal reaches an extremely high level due, for instance, to too much light -entering the scanning or camera tube and tending to cause saturation effects therein. When such conditions occur, the switch arm 55 ymay be moved to its lowercontact position at 4 contact 59, and a control voltage will then be supplied by way of the conductor 6| (with' the control voltage being determined by the energy ilow through the diode l) to vary the current flow through the relay winding 53 and thereby draw the magnetic control element G5, for operating the iris or diaphragm |1, further into the coil, or permits its retraction under the influence vof a, suitable resilient means (not shown for simplicity of diagram). Various ways and means to control the iris or diaphragm i1 may be provided, including ievels, racks and pinions and the like. each of which is well known in the art and thus requires no further illustration than the schematic one shown.

In an alternative form of system, the switch 51 may connect conductor 6| in parallel with the energy supply through resistor 53 to control the line amplifier 2|, so that the control effect may become effective both on the iris or diaphragm and the line amplifier unit.

While it has been above suggested that the current flowing in the relay winding 63 is particularly adapted for controlling the opening of the iris or diaphragm l1, it will also be apparent that a somewhat equivalent effect may be achieved by causinga substantial increase in the current in the relay winding to move progressively darker light absorbing filters intermediate the optical y system I5 and the opening to the scanning or camera tube through which the light of the optical image enters. Filters of this general type are, per se, generally known and require no specific description. The filters may be arranged on a disc in sector shaped sections and, for varying strengths of current flowing in the relay winding, the filter sections may be moved in stepped manner into the optical path. Alternatively, the filters may be arranged in a strip formation and, by virtue of different current strengths flowing in the relay winding 63, drawn down through the optical path and, with decreases in current, caused to move in the opposite direction under the influence of suitable resilient means, for example. It should be borne in mind, in this connection, that the light enters through a relatively narrow area and, by locating the lter closer adjacent the lens. the desired light gradations on the camera tube may be obtained.

Having now described the invention, what is claimed is:

1. In a television system wherein both video and intermittently present control signals are developed with the control signals occurring for time durations relatively short as compared with the time between successive control signals. means to amplify the video signals, means to combine the amplified video signals and the said control signals, an output amplifier for amplifying the said combined signals, a load circuit connected to receive the amplified combined signals from the output amplifier, a rectifier unit connected to receive also the combined video and control signals from the said combining means and to be rendered operative thereby to draw current to produce a control voltage which is proportional to the average current flowing, means for supplying the produced control voltage from the rectifier to each of the video amplifier and the output amplifier to control the amplification of each,

2. In a television system wherein both video and control signals are developed with the control signals occurring in spaced time relationship for time durations relatively short as compared with the time between successive control signals,

means to amplify the video signals, means to combine the amplified video signals and the said control signals, an output amplier for amplifying thev said combinedsignals, a load circuit connected to receive the amplied combined signals from the output amplier, a diode rectier unit having its anode element connected to receive also the combined video and control signals from the said combining means and its ycathode conoperative to produce control voltages during time nected to a point ot xed potential, vvhereb:- the diode is rendered operative during signal periods to draw current to produce control voltages proportional to the average current ilowing., means for supplying the produced control voltage from the diode toeach of the video amplifler and the output amplifier to provide an automatic volume control of the amplification of each, and means to supply the control signals to the diode rectier cathode circuit independently of the supply of the combined video and control signals to key the diode and render the said`d1ode rectier inperiods coinciding'with the presence oi the control signals in the combined signal.

` 1 Y. e, J. Pwr-I. 

